Diaphragm pumps



1965 D. M. s. GREENHALGH ETAL 3,166,239

DIAPHRAGM PUMPS Filed June 12. 1961 FIG].

United States Patent M This invention relates to diaphragm pumps and hasone applicaton in sampling air for radioactive dust.

To assess the average concentration of radioactive dust to which workersare exposed, it is known practice to take samples during the workingweek at fixed points in the operating areas. This method can yieldreliable information when the air flow pattern is well established andthe source of contamination is in a fixed place, but it is sometimesnecessary to determine the exposure of workers who are engaged in anumber of operations or working in a variety of places. Under suchconditions, air sampling at fixed points can give little indication ofthe true exposure.

A solution to this ditiiculty would be for each worker to carry aportable personal air sampler having a filter which would be examinedregularly, say weekly, for radioactivity. However the high powerrequirements of most existing long-term samplers have made themdependent on some external power supply such as electrical mains, andtherefore unsuitable for personal use.

It is an object of the present invention to provide a diaphragm pump,suitable for use in an air sampler, Whose power requirements aresufficiently low to enable it to be powered by portable batteries.

According to the present invention, in a diaphragm pump the diaphragmhas an aperture, an attachment member located in said aperture, saidmember slidably engaging a peripheral region of the diaphragmsurrounding the aperture, and means for imparting to the attachmentmemher a reciprocating movement normal to the plane of the diaphragm.

The attachment member may comprise two discs having the peripheralregion located between them.

The means for imparting the reciprocating movement may comprise aconnecting rod having one end connected to the attachment member, and arotatable crank connected to the other end of the connecting rod.

To enable the nature of the present invention to be more readilyunderstood, attention is directed, by way of example, to theaccompanying drawings wherein:

FIG. 1 is a cross-sectional elevation of a diaphragm pump embodying thepresent invention.

FIG. 2 is an enlarged, slightly exaggerated, fragment of FIG. 1, and

FIG. 3 is a perspective cut-away view of a portable air samplerincluding the pump of FIG. 1.

Referring to FIGS. 1 and 2, the pump comprises a head 1 made of methylmethacrylate, having an inlet port 2 and an outlet port 3. These portsare closed by flap valves 4 and 5 respeetivley, consisting of pieces ofaluminised polyethylene terephthalate film 0.00025 inch thick adhesivelysecured to the head 1. FIG. 1 shows the inlet valve 4 closed and theoutlet valve 5 open.

Spaced from the head by a polyethylene ring 6 is a diaphragm 7 made of0.004 inch polytetrafiuoroethylene (PTFE) sheet. The outer perpihery ofthe diaphragm is clamped between the ring 6 and a brass ring i2 byscrews 3 (FIG. 3). In the centre of the diaphragm is a circularaperture, the peripheral region of which is engaged by an attachmentmember comprising a bushing 9 having a rebate which passes through theaperture and through central holes in two PTFE discs 10 and 11, 0.01inch thick, between which the diaphragm is located. The aper- 3,166,239Patented Jan. 19, 1965 ture in the diaphragm is the samediameter as theholes in the discs. The discs and diaphragm are held in the rebate by awasher 13 and bolt 14, and as the rebate is 0.032 inch long whereas thethickness of the diaphragm plus discs is 0.024 inch, the diaphragm isfree to slide radially between the discs without permitting appreciableair leakage. The low-friction properties of PTFE facilitate the slidingaction.

'Fastened to the bushing 9 by the bolt 14 is an alu- -miniumconnecting-rod 15, in whose other end is held a low-friction bearing 16made of a dry-bearing material.

The bearing 16 is engaged by a crank pin 17 mounted ec-- centrically onthe face of a cylindrical polyethylene block 18 fastened to the shaft ofan electric motor 19 (FIG. 3). Rotation of the motor shaft thus causesthe attachment member at the centre of the diaphragm to reciprocate,drawing air in through the port 2 and expelling it through the port 3.The freedom of the diaphragm to slide between the discs 10 and 11reduces the torque required from the motor, since the reciprocation doesnot involve appreciable stretching of the diaphragm. This constructionalso strengthens the centre of the diaphragm.

In the present embodiment the diaphragm is inch in diameter and theamplitude of the reciprocation is 0.1 inch. The motor is a 6 voltconstant-speed motor running at about 1700 r.p.m. from mercury typebatteries.

FIG. 3 also shows the sampling head 20 which is connected to the inletport 4 by a length of flexible tubing 21. The sampling head supports aglass-fibre filter paper or membrane filter 22 of 1.5 cm. effectivediameter.

As the flow-rate remains sensibly constant during the working week, thevolume of air sampled can be determined from the sampling time. This canbe measured if desired by a 6 volt clock movement (not shown) operatedin parallel with the pump.

The sampling head may be secured to a button-hole or attached to theworkers clothing by a safety pin. The motor/pump unit and batteries arecontained in a case which is either carried in a pocket or in a pouch ona belt worn round the Waist.

We claim:

1. In a diaphragm pump, a diaphragm having an aperture, an attachmentmember located in said aperture, said member having an annular portionin interleaved slidable engagement with a peripheral region of thediaphragm surrounding the aperture, and means for imparting to theattachment member a reciprocating movement normal to the plane of thediaphragm.

2. A pump as claimed in claim 1 wherein the attachment member comprisestwo discs having said peripheral region located between them.

3. A pump as claimed in claim 2 wherein the means for imparting thereciprocating movement comprises a connecting rod having one endconnected to the attachment member, and a rotatable crank connected tothe other end of said rod.

4. An air sampler comprising a diaphragm pump including a diaphragmhaving an aperture, an attachment member located in said aperture, saidmember having an annular portion in interleaved slidable engagement witha peripheral region of the diaphragm surrounding the aperture, and meansfor imparting to the attachment member a reciprocating movement normalto the plane of the diaphragm.

5. An air sampler as claimed in claim 4 wherein the attachment membercomprises two discs having said peripheral region located between them.

6. An air sampler as claimed in claim 5 wherein the means for impartingthe reciprocating movement comprises a connecting rod having one endconnected to the attachment member and a rotatable crank connected tothe other end of said rod.

7. A diaphragm pump comprising a pump head having an inlet port With aflap valve and an outlet port with a flap valve, a diaphragm having anaperture, means clamping the perimeter of said diaphragm to said pumphead, an attachment member located in said aperture, said attachmentmember including parts-spaced apart to engage the opposed surfaces ofsaid diaphragm adjacent to said aperture, the spacing of said partsbeing greater than the thickness of said diaphragm, and means forimparting to the attachment member a reciprocating movement normal tothe plane of the diaphragm.

8. A diaphragm pump comprising a pump head having inlet and'outletports, a diaphragm having a central aperture, means clamping theperimeter of said diaphragm to said pump head, an attachment memberlocated in said central aperture, said attachment member including partsspaced apart to engage the opposed surfaces of said diaphragm adjacentto said aperture, the spacing between said parts being greater than thethicknes of said diaphragm, a driver connected to said attachment memberto extend normal to the plane of said diaphragm, and means to impartreciprocation to said driver to flex said diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS1,767,320 Sinanide June 24, 1930 2,253,206 Farrow Aug. 19, 1941 FOREIGNPATENTS 855,286 Great Britain Nov. 30, 1960

1. IN A DIAPHRAGM PUMP, A DIAPHRAGM HAVING AN APERTURE, AN ATTACHEMENTMEMBER LOCATED IN SAID APERTURE, SAID MEMBER HAVING AN ANNULAR PORTIONIN INTERLEAVED SLIDABLE ENGAGEMENT WITH A PERIPHERAL REGION OF THEDIAPHRAGM SURROUNDING THE APERTURE, AND MEANS FOR IMPARTING TO THEATTACHMENT MEMBER A RECIPROCATING MOVEMENT NORMAL TO THE PLANE OF THEDIAPHRAGM.